Fuel cell module comprising a magnetic shielding

ABSTRACT

A fuel cell module includes a plurality of fuel cells, which are connected one behind the other and which are combined to form a fuel cell stack. The fuel cell module should be designed in such a manner that the magnetic field or leakage field, which can be detected in the outer area and which is generated during the operation of the fuel cell module, is held at a particularly low level. To this end, the materials used for providing the fuel cells themselves, the materials used for producing the connecting components or auxiliary components, which are assigned thereto, that connect these fuel cells, and the materials used for producing the housing are selected that have a relative magnetic permeability of less than 1.1.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/DE01/04392 which has an Internationalfiling date of Nov. 21, 2001, which designated the United States ofAmerica and which claims priority on German Patent Application number DE100 59 568.5 filed Nov. 30, 2000 the entire contents of which are herebyincorporated herein by reference.

FIELD OF THE INVENTION

The invention generally relates to a fuel cell module having a number offuel cells arranged in a housing and electrically connected in series.

BACKGROUND OF THE INVENTION

Fuel cells can be used for the environmentally friendly generation ofelectricity. In a fuel cell, a process which substantially represents areversal of electrolysis takes place. For this purpose, in a fuel cell,a fuel which includes hydrogen is fed to an anode. Further, an auxiliarysubstance which includes oxygen is fed to a cathode. The anode andcathode are electrically separated from one another by an electrolytelayer.

Although the electrolyte layer allows ion exchange between the fuel andthe oxygen, it otherwise ensures gastight separation of the fuel andauxiliary substance. As a result of the ion exchange, hydrogen which ispresent in the fuel can react with the oxygen to form water, withelectrons accumulating at the fuel-side electrode or anode and electronsbeing taken up at the electrode on the side of the auxiliary substance,or the cathode.

Therefore, when the fuel cell is operating, a usable potentialdifference or voltage builds up between anode and cathode, while theonly waste product of the electricity generation process is water. Theelectrolyte layer, which in the case of a high-temperature fuel cell maybe formed as a solid ceramic electrolyte or in the case of alow-temperature fuel cell may be formed as a polymer membrane, thereforehas the function of separating the reactants from one another,transferring the charge in the form of ions and preventing an electronshort circuit.

A fuel cell comprises a flat electrolyte, one flat side of which isadjoined by a flat anode and the other flat side of which is adjoined bya cathode, which is likewise flat. These two electrodes, together withthe electrolyte, form what is known as an electrolyte electrodeassembly. Adjacent to the anode there is an anode gas space, andadjacent to the cathode there is a cathode gas space.

An interconnector plate is arranged between the anode gas space of afuel cell and the cathode gas space of a fuel cell adjacent to this fuelcell. The interconnector plate produces an electrical connection betweenthe anode of the first fuel cell and the cathode of the second fuelcell. Depending on the type of fuel cell, the interconnector plate isdesigned, for example, as a single metallic plate or as a coolingelement which comprises two plates stacked on top of one another with acooling-water space between them. Depending on the type of fuel cell,there are further components, such as for example electricallyconductive layers, seals or pressure cushions, in a fuel cell stack.

On account of the electrochemical potentials of the materials which arecustomarily used, in a fuel cell of this type an electrode voltage ofapproximately 0.6 to 1.0 V can be built up under normal operatingconditions and maintained during operation. For industrial applications,in which a significantly higher total voltage may be required, dependingon the intended use or the planned load, therefore, it is customary fora plurality of fuel cells to be electrically connected in series in theform of a fuel cell stack. The fuel cells are stacked in such a mannerthat the sum of the electrode voltages supplied by the fuel cellscorresponds to the required total voltage or exceeds this total voltage.Depending on the total voltage required, the number of fuel cells in afuel cell stack of this type may, for example, amount to 50 or more.

To make it possible to utilize the potential difference generated whenthe fuel cells which have been connected up to form a fuel cell stack ofthis type are operating, the fuel cell stack is connected to a load. Inthis case, for electrical connection of the load to the fuel cell stack,there is what is known as a terminal plate, to which electrical supplyand discharge lines can be connected, arranged at the two outermost fuelcells of the fuel cells which are connected in series.

On account of the particular operating properties of fuel cells of thistype, and in particular since water is the only significant by-productproduced, fuel cells are also particularly suitable for use forsupplying energy in closed mobile systems, such as for exampleunderwater vessels. In this context, it is particularly advantageousthat a relatively high output current can be achieved at a standardvoltage level in the form of a relatively high power density in a fuelcell arrangement with only limited spatial dimensions. Moreover,particularly for use in underwater vessels, the fuel, i.e. the substancewhich includes hydrogen, can be provided in relatively compact form. Theauxiliary substance or oxidizing agent used may in this case be pureoxygen. The hydrogen may in this case in particular be carried along inhydride tanks.

Particularly when fuel cells are used in an underwater vessel, it may bedesirable for the signature emitted to the outside, i.e. the externallydetectable signs indicating the location or operation of the underwatervessel, to be kept at a particularly low level. This signature may alsoinclude magnetic fields which are generated by the currents flowing inand out when fuel cells are operating.

SUMMARY OF THE INVENTION

Therefore, an embodiment of the invention is based on an object ofproviding a fuel cell module having a number of fuel cells which arearranged in a housing and are electrically connected in series. Further,the magnetic field or leakage field which can be detected in its outerregion is kept at a particularly low level.

According to an embodiment of the invention, an object may be achievedby both the housing and the terminal plates and the interconnectorplates being made from materials which have a relative magneticpermeability (μ_(r)) of less than 1.1.

The relative permeability μ_(r) is in this case a material-dependentproportionality constant between the magnetic field strength H and themagnetic induction or flux density B. The relative magnetic permeabilityμ_(r) in particular indicates how the material in question contributesto the overall magnetic field strength H produced in response to apredetermined external magnetic flux density B as a result of itsstructural or molecular properties.

An embodiment of the invention is based on the consideration that themagnetic field which can be detected in the outer region of the fuelcell module may be composed of both active and passive contributions. Tokeep the magnetic field which can be detected in the outer region of thefuel cell module at a particularly low level, therefore, both of thesecontributions should be kept at particularly low levels independently ofone another. With regard to the active contributions, which are induced,for example, by the operating current when the fuel cell module isoperating, this can result in design stipulations relating to thepassage of current when the fuel cell module is operating.

In addition, however, the passive contribution, i.e. the component whichis additionally formed in response to an externally predeterminedmagnetic field or in response to the magnetic field generated by theoperating current which is flowing, should also be kept at aparticularly low level. One measure of a contribution of this type isthe relative magnetic permeability μ_(r). Therefore, the materials ofthe fuel cell module are selected in such a manner that their relativemagnetic permeability μ_(r) and therefore the contribution which occursin response to a predetermined magnetic field is kept at a particularlylow level.

Examples of advantageous materials are nonmetallic materials oraustenitic steels. They have the required low permeability and areparticularly resistant to chemical attacks.

It is expedient for both the materials which are used to provide thefuel cells per se and the materials which are used to produce connectingcomponents which connect the fuel cells, or associated auxiliarycomponents, and the materials used for the housing to have a relativemagnetic permeability of less than 1.1. As a result, relatively highlymagnetic materials and therefore a high signature are avoidedaltogether.

Each fuel cell usually includes a number of carrier cards, which arealso referred to as cooling cards, each enclose gas and/or coolantspaces and are provided with a contact plate. These functionalcomponents, which are of significance to the actual fuel cell, areadvantageously formed from a graphite-doped plastic body provided with aprotective layer based on Ti. In this case, on the one hand the choiceof the plastic-bonded graphite as the main material for theabovementioned components ensures that these components have aparticularly low relative magnetic permeability μ_(r) and are thereforesubstantially completely nonmagnetic. On the other hand, the protectivelayer which is based on Ti ensures that the respective functionalcomponent can be operated even in a relatively aggressive atmosphere orenvironment without being significantly adversely affected. This isbecause when the fuel cell is operating these components are usuallyexposed to a relatively aggressive atmosphere, for example a pure oxygenatmosphere, and consequently it is necessary to reckon with high levelsof corrosion.

To make the abovementioned components able to resist corrosion of thistype even when plastic-bonded graphite is selected as the main material,they are advantageously provided with a protective layer based on Ti, inthe form of a passivation.

In an alternative or additional advantageous configuration, thosecomponents of the fuel cell module which, during operation, are exposedto contact with a reactant of the or each fuel cell are, at least in asurface region, made from an alloy based on nickel. This is becauseselecting a material of this type firstly ensures that the relativemagnetic permeability μ_(r) can be kept at a particularly low level.

Secondly, a material of this type is relatively insensitive to corrosionand can therefore operate reliably even in contact with the relativelyaggressive atmosphere of the reactants with a particularly longoperating time. Accordingly, in particular the components which aredirectly exposed to the electrochemical process in a fuel cell, such asfor example terminal plates, busbars and/or interconnector plates, suchas cooling cards, may be made from a nickel-based alloy of this type.

In a further advantageous configuration, the surface region has analloying constituent of approximately 50% or more of nickel. In thiscase, it is possible in particular to use a nickel-based alloy which isalso known as Hastelloy and comprises as alloying constituentsapproximately 50% of Ni, 15% of Cr, 15% of Mo and a relatively smallamount of Fe. An alloy of this type has a relative magnetic permeabilityμ_(r) of less than 1.08 and is therefore particularly suitable for usein the fuel cell module. Alternatively, the Cr constituent could also bereplaced by another suitable component.

Within a fuel cell module, the actual fuel cells are usually alsoassigned auxiliary components, referred to as operating parts, orprocess technology devices, such as, for example, valves, measuringequipment, sensors, pipes, flexible tubes or separators. These auxiliarycomponents, unlike the core components listed above, are not directlyexposed to the reactants or the electrochemical process when the fuelcell module is operating.

In order, on the one hand, to reliably ensure that these auxiliarycomponents have a sufficiently low magnetic permeability μ_(r) and onthe other hand to also keep production outlay at a particularly lowlevel, these auxiliary components are preferably made from stainlesssteel. In particular, they are preferably made from a stainless steelwhich can only be magnetized to a very small extent or an alloy based onnickel. If the auxiliary components are based on nickel, their materialadvantageously includes an alloying constituent of approximately 50% ofNi. Therefore, in a particularly advantageous configuration, theabovementioned material, which is also known as Hastelloy, is also usedfor these components.

If the abovementioned auxiliary components are made from stainlesssteel, the material used is advantageously a nitrogen-stabilizedstainless steel which can only be magnetized to a very slight extent andwhich is available as material type 1.3954, 1.3964 or 1.3974. Furtherstainless steels of this type which may be suitable are those which bearthe designations 1.3802, 1.3805, 1.3813, 1.3815, 1.3817, 1.3819, 1.3941,1.3949, 1.3952, 1.3953, 1.3958, 1.3960, 1.3962, 1.3965, 1.3967 and1.3968.

The advantages achieved by at least one embodiment of the inventionreside, in particular, in the fact that, as a result of exclusivelymaterials which have a low relative magnetic permeability μ_(r) of lessthan approximately 1.1 being selected both for the fuel cells per se andfor the connecting or auxiliary components used and also for the housingof the fuel cell module, the components or parts can only be magnetizedto a relatively slight extent. Therefore, these components or theirmaterial only cause a relatively slight amplification of the magneticfield which is present locally and generated by external influences orelse by the operating current. Therefore, the fuel cell module has aparticularly insignificant signature in its outer region.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is explained in more detailwith reference to a drawing, in which:

The FIGURE diagrammatically depicts a fuel cell module.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The fuel cell module 1 shown in the FIGURE comprises a plurality of fuelcells 2 which are combined in the form of a fuel cell stack and whichare electrically connected in series. The fuel cells 2 form a fuel cellblock which is surrounded by an inner housing 4 and is electricallyconnected to an electric load (not shown in more detail) on the inputside via a line 6 and on the output side via a line 8.

The fuel cells 2 which are connected up to form the fuel cell stack areassigned a number of auxiliary components (not shown in more detail),such as valves, measuring equipment, sensors, tubes, pipes orseparators, which are arranged in a common housing segment 10 outsidethe inner housing 4. The inner housing 4 and the housing segment 10mounted on it are arranged in an outer housing 12 which surrounds themjointly in the manner of a jacket housing and which is used to protectthe fuel cell module 1 both mechanically and against leaks. The lines 6,8, in a connection region, are guided through a connection piece 14flanged onto the outer housing 12 into the outer region of the housing12.

When it operates, the fuel cell module 1 is designed to generate aparticularly low signature level which can be detected externally. Forthis purpose, the fuel cell module 1 is designed in such a manner that,when it operates, both the magnetic field which is actively generated bythe operating current I, denoted by arrow 16 in the FIGURE, and theadditional magnetic field generated by the response of the materials tothis magnetic field or a magnetic field which is externally imposed arekept at particularly low levels. For this purpose, on the one hand thelines 6, 8 and further line sections and components (not shown in moredetail in the exemplary embodiment) are arranged in such a manner thatthe magnetic fields generated by the currents flowing therein in theouter region are substantially compensated for and therefore there isonly a particularly low residual magnetic field. To keep thecontribution made by the fuel cell module 1 with regard to the passivemagnetic fields at a particularly low level as well, furthermore, allthe materials used are selected in such a manner that they have arelative magnetic permeability μ_(r) of less than 1.1.

For this purpose, both the materials used to provide the fuel cells 2per se and the materials used to produce connecting components whichconnect the fuel cells 2 or the auxiliary components arranged in thehousing segment 10 and the materials used for the inner housing 4, thehousing segment 10 and the outer housing 12 are selected with acorrespondingly low relative magnetic permeability μ_(r).

The fuel cells 2 have interconnector plates, which are also referred toas carrier cards and which are designed as cooling cards. They surrounda cooling-water space and, with the aid of passages or stampedstructures, in combination with one another or in combination with theelectrolyte electrode assembly, form gas spaces through which the fuel(a hydrogen-containing gas) and the auxiliary substance (anoxygen-containing gas) flow. These plates are mainly formed from agraphite-doped plastic body. This plastic body, which is also referredto as plastic-bonded graphite, is virtually nonmagnetic and has arelative magnetic permeability μ_(r) of approximately 1.0.Alternatively, it is also possible for the main material used to be analloy based on nickel or a stainless steel. In order for thesecomponents, which during operation are exposed to the electrochemicalprocesses and therefore to a particularly aggressive atmosphere from thereactants, additionally also to be designed for a particularly longoperating time, the plastic body is in each case provided with aprotective layer based on titanium. The terminal plates are made from analloy based on nickel. In this case, the material used is an alloywhich, as alloying constituent, contains 50% of Ni, 15% of Cr, 15% of Moand a small residual quantity of Fe and is also known as Hastelloy.

The auxiliary components arranged in the housing segment 10 may likewisebe made from a nickel-based alloy of this type.

In the exemplary embodiment, however, the auxiliary components are madefrom stainless steel, in which case, on the one hand, there is likewisea particularly low relative magnetic permeability μ_(r) and also, on theother hand, the corrosion resistance is sufficient in particular for usein the housing segment 10. For this purpose, the auxiliary componentsare made from stainless steel which cannot be magnetized and isparticularly stabilized by the addition of nitrogen. In the exemplaryembodiment, the material provided is the stainless steel available undermaterial number 1.3964. Alternatively, however, it is also possible touse the stainless steel available under material number 1.3954 ormaterial number 1.3974.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A fuel cell module, comprising: a fuel cell stack including aplurality of fuel cells electrically connected in series, arranged in aninner housing, and delimited by two terminal plates, wherein theplurality of fuel cells form a fuel cell block, each of the fuel cellsincluding an electrolyte electrode assembly adjoined by twointerconnector plates, wherein the inner housing, the terminal platesand the interconnector plates are made from materials which have arelative magnetic permeability of less than 1.1 and the twointerconnector plates are designed as cooling cards that surround acooling-water space, and said two terminal plates are conductors forelectrically connecting a load to the fuel cell stack.
 2. The fuel cellmodule as claimed in claim 1, wherein the inner housing, the terminalplates and the interconnector plates are made from a material selectedfrom the group consisting of nonmetallic materials and austenitic steel.3. The fuel cell module as claimed in claim 1, wherein the materialsused to provide the fuel cells, the materials used to produce at leastone of connecting components which connect them and associated auxiliarycomponents, and the materials used for the inner housing, include arelative magnetic permeability of less than 1.1.
 4. The fuel cell moduleas claimed in claim 1, wherein the cooling cards enclose at least one ofgas and the cooling-water space, and are provided with a contact plate.5. The fuel cell module as claimed in claim 1, wherein components whichare exposed to contact with a reactant of at least one fuel cell duringoperation, are produced, at least in a surface region, from an alloybased on nickel.
 6. The fuel cell module as claimed in claim 5, whereinthe surface region includes an alloying constituent of approximately 50%of Ni.
 7. The fuel cell module as claimed in claim 1, wherein auxiliarycomponents of the fuel cell module are made from a material selectedfrom the group consisting of stainless steel and an alloy based onnickel.
 8. The fuel cell module as claimed in claim 7, wherein thematerial of the auxiliary components includes an alloying constituent ofapproximately 50% of Ni.
 9. The fuel cell module as claimed in claim 7,wherein the auxiliary components are made from a stainless steelselected from the group consisting of type 1.3954, 1.3964 and 1.3974.10. The fuel cell module as claimed in claim 2, wherein the materialsused to provide the fuel cells, the materials used to produce at leastone of connecting components which connect them and associated auxiliarycomponents, and the materials used for the inner housing, include arelative magnetic permeability of less than 1.1.
 11. The fuel cellmodule as claimed in claim 2, wherein the cooling cards enclose at leastone of gas and the cooling-water space, and are provided with a contactplate.
 12. The fuel cell module as claimed m claim 3, wherein thecooling cards enclose at least one of gas and the cooling-water space,and are provided with a contact plate.
 13. The fuel cell module asclaimed in claim 2, wherein components which, during operation areexposed to contact with at least one of a reactant and each fuel cell,are produced, at least in a surface region, from an alloy based onnickel.
 14. The fuel cell module as claimed in claim 13, wherein thesurface region includes an alloying constituent of approximately 50% ofNi.
 15. The fuel cell module as claimed in claim 2, wherein auxiliarycomponents of the fuel cell module are made from a material selectedfrom the group consisting of stainless steel and an alloy based onnickel.
 16. The fuel cell module as claimed in claim 15, wherein thematerial of the auxiliary components includes an alloying constituent ofapproximately 50% of Ni.
 17. The fuel cell module as claimed in claim15, wherein the auxiliary components are made from a stainless steelselected from the group consisting of type 1.3954, 1.3964 and 1.3974.18. The fuel cell module as claimed in claim 3, wherein componentswhich, during operation are exposed to contact with at least one of areactant and each fuel cell, are produced, at least in a surface region,from an alloy based on nickel.
 19. The fuel cell module as claimed inclaim 18, wherein the surface region includes an alloying constituent ofapproximately 50% of Ni.
 20. The fuel cell module as claimed in claim 3,wherein auxiliary components of the fuel cell module are made from amaterial selected from the group consisting of stainless steel and analloy based on nickel.
 21. The fuel cell module as claimed in claim 20,wherein the material of the auxiliary components includes an alloyingconstituent of approximately 50% of Ni.
 22. The fuel cell module asclaimed in claim 20, wherein the auxiliary components are made from astainless steel selected from the group consisting of type 1.3954,1.3964 and 1.3974.
 23. A fuel cell module, comprising: an inner housing;and a plurality of fuel cells, electrically connected in series forminga fuel cell stack, arranged in the inner housing, wherein the pluralityof fuel cells form a fuel cell block, wherein the fuel cell stack isdelimited by two terminal plates, said two terminal plates beingconductors for electrically connecting a load to the fuel cell stack,and further wherein the inner housing, the two terminal plates, the fuelcells and interconnections of the fuel cells are made from materialswhich have a relative magnetic permeability of less than 1.1, and theinterconnections designed as cooling cards that surround a cooling-waterspace.
 24. The fuel cell module of claim 23, further comprising aplurality of auxiliary components, associated with the fuel cell stackand arranged in a housing segment outside the inner housing.
 25. Thefuel cell module of claim 24, wherein the auxiliary components and thehousing segment are made from materials which have a relative magneticpermeability of less than 1.1.
 26. The fuel cell module of claim 25,further comprising an outer housing, surrounding both the inner housingand the housing segment.
 27. The fuel cell module of claim 26, whereinthe outer housing is made from materials which have a relative magneticpermeability of less than 1.1.
 28. The fuel cell module of claim 23,wherein each of the fuel cells include an electrolyte electrode assemblyadjoined by two interconnector plates, each made from materials whichhave a relative magnetic permeability of less than 1.1.
 29. The fuelcell module of claim 28, further comprising a plurality of auxiliarycomponents, associated with the fuel cell stack and arranged in ahousing segment outside the inner housing, wherein the auxiliarycomponents and the housing segment are made from materials which have arelative magnetic permeability of less than 1.1.
 30. The fuel cellmodule of claim 29, further comprising an outer housing, surroundingboth the inner housing and the housing segment, wherein the outerhousing is made from materials which have a relative magneticpermeability of less than 1.1.
 31. The fuel cell module as claimed inclaim 25, wherein auxiliary components of the fuel cell module are madefrom a material selected from the group consisting of stainless steeland an alloy based on nickel.
 32. The fuel cell module as claimed inclaim 31, wherein the material of the auxiliary components includes analloying constituent of approximately 50% of Ni.
 33. The fuel cellmodule as claimed in claim 31, wherein the auxiliary components are madefrom stainless steel selected from the group consisting of type 1.3954,1.3964 and 1.3974.
 34. The fuel cell module as claimed in claim 4,wherein the plurality of carrier cards are each formed from agraphite-doped plastic body provided with a protective layer based onTi.
 35. The fuel cell module as claimed in claim 11, wherein theplurality of carrier cards are each formed from a graphite-doped plasticbody provided with a protective layer based on Ti.
 36. The fuel cellmodule as claimed in claim 12, wherein the plurality of carrier cardsare each formed from a graphite-doped plastic body provided with aprotective layer based on Ti.
 37. The fuel cell module of claim 1,further comprising a plurality of auxiliary components associated withthe fuel cell stack, the auxiliary components being arranged in ahousing segment outside the inner housing.
 38. The fuel cell module ofclaim 37, wherein the auxiliary components and the housing segment aremade from materials which have a relative magnetic permeability of lessthan 1.1.
 39. The fuel cell module of claim 37, further comprising anouter housing wherein the inner housing and the housing segment arearranged in the outer housing.
 40. The fuel cell module of claim 39,wherein the outer housing is made from materials which have a relativemagnetic permeability of less than 1.1.